Surge Anticipator Eliminates Pipe Breakage in Central Saanich

The District of Central Saanich in British Columbia is a rural residential community with a population of about 17,000. The district has a medium sized, widely dispersed sewerage collection system dating back to the early 1970s that sends its sewage for treatment to the regional wastewater treatment plant. There is minimal storage capacity within the municipal collection system, with multiple sewage lift stations pumping sewage from these satellite stations through force mains to treatment.

One of these facilities pumps sewage through a 300 mm asbestos cement force main to a sewer siphon several kilometers away. When fluids travel such long distances, there is always the potential for pressure build-up from even the slightest changes in velocity.

Due to aging infrastructure and surges from pumps stopping and power failures, the sewer main was rupturing, causing costly repairs and negative effects on the environment and residents. Engineers recommended installing an anticipating surge relief valve to reduce stress on the pipes and thus prevent bursts.

Central Saanich has three 75-hp pumps that each cycle between 30 and 50 times a day. As the valve operates on every shutdown, it is crucial that the valve operation be precise and occur at the right times to prevent surges, otherwise lines could literally be blown out of the ground.

The Pneumatic Dynamic Lifter is a very responsive compact sewage relief valve that can handle high pressures (200 psi or 13.8 bar or higher) and uses standard plant air supply to hold the valve closed. The chamber is fitted with a relief pilot that is also normally closed as long as the line pressure is lower than the set point. If pressure rises above the set point, the relief pilot opens, causing the air in the cylinder to vent, which in turn opens the valve. So this operates as a high-pressure relief valve.

Another problem that Central Saanich had was surges due to power interruptions. When this happens, all the pumps suddenly stop, resulting in a severe surge (proportional to fluid velocity at the time of the power interruption). Singer Valve was the only company that had a Pneumatic Dynamic Lifter with the solenoid operated surge anticipator that would still work during power outages.

The anticipating surge relief function has two 3-way solenoid valves to put air into the cylinder under the piston, driving the valve open on power failure. This way when the surge returns back to the pump it is not coming back to a closed system where it can cause damage; it comes back to an open valve where it can be discharged safely back into the storage well underneath the pump. The main valve needs to be open long enough to handle the initial surge but not longer, otherwise it will continue to drain the line. To prevent this, the solenoid is on a timer, which the field crew sets at start up. Once the timer has elapsed, then another solenoid allows air to recharge the cylinder, thus closing the main valve.

With Singer’s Surge Anticipating Pneumatic Dynamic Lifter, Central Saanich was able to successfully eliminate surges on pump shut downs and during power failures.

Singer Valve is exhibiting at WEFTEC.16, Booth 7129. For more information, visit www.singervalve.com.